Foldable phones are often equipped with two displays: a large-sized first display for use mainly in an open-folded position and a smaller second display for use mainly in a closed-folded position. The second display (called a sub-display herein after) is typically used for displaying time/date, who is calling, message received or other similar status info.
Traditionally large-sized displays (called a main display herein-after) for displaying a menu, an image or a picture have been provided to mobile phones, and nowadays further sub-displays for displaying sub-information or secondary information are becoming even more popular. In such a mobile phone that has the above-mentioned configuration, it is possible to significantly improve the usability of a thus configured mobile phone by selectively displaying information on the main display and the sub-display.
Among those mobile phones having such a sub-display, there is a folding type (sometimes called a clamshell-type) mobile phone, wherein the mobile phone has a main display provided inside of an upper housing, and a sub-display provided on the top surface of a lower or a upper housing, and a hinge that enables the upper housing and the lower housing to open/close so as to cover the respective top surfaces of each other.
In the mobile phone configured as above, the sub-display is configured to be exposed to the outside even in a closed position of the housings. When the housings are opened in order, for example, to make a call, at least the main display is exposed to the user. When the housings are closed for carrying the device, the main display is usually covered but the sub-display is exposed to the user, and accordingly, it is able to provide the user some information irrespective of the opening/closing of the housings.
Other types of mobile devices comprising main displays and sub-displays are also known. Such devices may comprise, instead or in addition to a traditional hinge, a slide or a swivel.
Supplying the device with a second display makes the mobile device thicker and also causes additional expenses. The overall complexity of the device increases significantly and this raises several mechanical and electrical issues.